The present invention relates to a technique for improving the DC-DC conversion efficiency of a synchronous rectifier type DC-DC converter and a technique for improving the conversion efficiency by reducing power loss during light load in a synchronous rectifier type switching regulator having a reverse current prevention function that detects a reverse current and controls transistors for synchronous control. In particular, the invention relates to the above techniques that are effectively applied to, for example, a supply voltage control device comprising switching elements constituting the switching regulator and a dive circuit thereof, its electronic component module for power supply (power supply driver module), and a power supply device.
A synchronous rectifier type switching regulator is one of DC-DC converters. The synchronous rectifier type switching regulator has a switching element located on a path for current flow from a power supply via a coil (inductor) to a load and controls the current flowing into the load by turning the switching element on and off. Moreover, the regulator has another switching element for synchronous rectification between a node connecting the above switching element and the coil and ground (a ground point) to reduce loss by complementary on/off control of this switching element with the main switching element.
Such a synchronous rectifier type switching regulator has a problem in which a useless power loss ratio increases as the load becomes light, whereas this ratio is small when the load is relatively heavy. This is due to that the direction of the current flowing through the coil is reversed as the load becomes light, which causes a negative current (reverse current) to flow through the switching element for synchronous rectification to the ground and results in a loss, whereas a positive current toward the load always flows through the coil during heavy load. To reduce the loss due to this reverse current, an invention arranged to detect a transition to a light load state in which the reverse current flows and turn the ground-side switching element for synchronous rectification off has been proposed (e.g., patent document 1).
[Patent document 1] Japanese Unexamined Patent Publication No. 2002-281743